Where do I find the API error messages?

Where do I find the API error messages?

We use a function.php script to connect the download form of our website to Zoho CRM. When a visitor submits their contact information on the download form, an email is sent to us and the data is inserted into Zoho automatically using the InsertRecords API method.

This function.php script was written by a freelance developer.

The script has been working fine for us. However, once in a while, we will have leads that don't get inserted into ZohoCRM.

I am trying to troubleshoot this issue with limited development knowledge. While reading others topic in this forum, I noticed people reporting API error messages and their error code. I can't seem to find where these error codes are displayed? Can someone point me to where I can view my XML errors so I can pinpoint the error that is preventing the record from being inserted into Zoho?

Thanks for your help!